In many elevator systems the elevator car door is coupled to the hall door at each floor to prevent the car from moving when the hall door is open and to enable the car door to open and close the hall door synchronously at the floor. U.S. Pat. No. 3,638,762 to Johns on a DOOR COUPLING APPARATUS FOR ELEVATORS, which is also assigned to the Assignee of this application, shows a device for that purpose. The previously mentioned copending application, also by Johns, on a MAGNETIC ROLLER, pertains to an enhanced version of that patented coupling device or apparatus.
Comprising two rollers, which are attached to the hall door, that apparatus operates in conjunction with a vertical vane, which is carried on the car door and which fits between these two rollers when the car is at the floor. As the car door opens, this vane pulls on one of the rollers, and this action couples the two doors together, and thus, as the car door opens, it opens the hall door. This roller also controls the position of a spring loaded arm, on which it is attached, and which, in response to the pressure of the vane, rotates to operate a switch which prevents the car from moving when the hall doors are even slightly open. This arm also locks the hall doors closed. In the reverse mode, as the car door closes, the vane pushes on the other roller. This action couples the two doors together and, thus, as the car door closes, it closes the hall door. When the hall door is just about fully closed, the previously mentioned arm rotates, operating the switch so as to permit the car to move, which it can do safely now that both doors are closed. For this arrangement to operate properly, the vane must be positioned between the two rollers when the car is at the floor. If it is not--if it is positioned on the outside, for example, which is known as a "door behind" condition--not only will the hoistway door not open as the car door opens, but the car door will not fully close. If that happens, car door position sensing apparatus, which are typical in most systems, will sense the partially open car door position and prevent the car from moving any further. The car is thus immobilized at the floor, with the car door slightly open and with the hall door fully closed. The only way to correct that is to move the car away from the floor, so that the car door can fully close, but, since the car is immobilized, that requires overriding the system's safety controls, which typically can be done only by a service technician.
The door behind condition does not occur frequently, but, as it can be appreciated, when it does happen, it may cause a lengthy service disruption which requires repair by a service technician. In most instances it happens because, at the floor, there is a temporary misalignment between the car door and the door coupling apparatus. One place it may occur is in elevator systems that have advanced car door opening sequences in order to reduce car flight time. It is possible, in those systems, that the car door may open too quickly, that is, too far in advance of the floor, and, thus, when the car reaches the floor, the door is open at a point where the vane is behind the roller.